1. Field of Endeavor
The present disclosure relates to a method for driving an IGBT, and more particularly to a method for driving an IGBT employed as a power device for a current limiter.
2. Background
The IGBT (Insulated Gate Bipolar Transistor) is a voltage-driven device through gate-emitter terminals that combines simple gate-drive characteristics of MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) with a high-current and low-saturation-voltage capability of BJTs (Bipolar Junction Transistors).
The IGBT has a high input impedance like the MOSFET, and a high-current and low-saturation-voltage capability of BJTs.
FIG. 1a is a schematic view illustrating symbols used in IGBT, where D refers to a diode, C refers to a collector, E refers to an emitter and G refers to a gate.
FIG. 1b is a graph illustrating a characteristic of turn-off at the IGBT. If a gate voltage surpasses a threshold voltage based on a gate electrostatic capacity, the IGBT is turned on, and turned off if the gate voltage goes down below the threshold voltage.
A collector-emitter voltage (VCE) generated during switching of IGBT is generated by transient voltage caused by stray inductance on a conductive line and input voltage. Thus, there is needed an IGBT driving technology capable of limiting a transient voltage level.
FIG. 2 is a schematic view illustrating an IGBT driving method according to prior art.
Referring to FIG. 2, a transient voltage Vce is generated across an IGBT in a parallel circuit where a conventional IGBT 100 and passive elements R, L and C 200 are connected in parallel during turn-off operation of a current flowing to the IGBT 100. The transient voltage has an absolute influence to damage of IGBT 100.
Snubber circuits 300 are connected in parallel to prevent the transient voltage in the conventional IGBT circuit. The term of snubber refers to an auxiliary circuit element or combination of elements used for alleviating the transient voltage in a semiconductor device. The snubber circuit is largely formed with an RC (Resistor-Capacitor) or an RCD (Resistor-Capacitor-Diode). However, the snubber circuit 300 needs much more number of passive power elements during high voltage design, such that the passive elements cause a problem of generating an additional loss during IGBT operation.